Due to the rapid advance of technology, many times electronic systems and devices become outdated in a short amount of time. In these cases, a person may buy a new electronic system, and no longer have a use for the original system. One way to salvage the original electronic system is to determine if it can be modified to make it perform like the new electronic system. If this may be accomplished by only exchanging a few electronic components, this may be a much simpler and less costly process than a new system. The problem arises if the new electronic component when inserted into the same location as an original electronic component, has the potential to cause problems in the electronic system even though the interconnections are the same.
FIG. 1 shows a schematic diagram of an example circuit in an existing electronic system with an IC (Integrated Circuit) 2 that includes a die 4 on a package 6. IC 2 attaches to a motherboard 8 through socket 10. Vcc voltage regulator 12 supplies Vcc voltage to the core circuits in IC 2. Vtt voltage regulator 14 supplies voltage to termination devices 16 that is connected to IC 2 GTL (Gunning Transceiver Logic) signal line 18. Therefore, GTL signal line 18 has a termination device connected to it that is mounted on motherboard 8. Although FIG. 1 shows only one signal line, this is representative of all GTL or open drain type signal lines of IC 2 that connect to other devices on motherboard 8. There may also be open drain signal lines that are not GTL signal lines. These signal lines may be capable of using a higher termination voltage than the GTL signal lines. For this reason, IC 2 may receive voltages from the Vcc voltage and the Vtt voltage and depending on the devices attached to the non-GTL signal lines, supply a non-GTL signal line termination voltage 20, that is either the Vcc voltage or the Vtt voltage, to the termination devices attached to non-GTL signals (e.g., CMOS signals).
If a person desires to upgrade the electronic system shown in FIG. 1 for improved performance and/or functionality, IC 2 might need to be replaced with another improved IC. The improved IC must be electrically compatible with IC 2 in order to be attached to motherboard 8. A problem may arise when the improved IC is compatible with IC 2, but has termination devices on the die of the improved IC. That is, when the improved IC is attached to motherboard 8, the GTL signal lines now have termination on the motherboard, and termination on the die of the improved IC and such termination resistors may cause a conflict or degradation in an operation of the circuit.
As description of one example problem, an improved IC with termination on the die (not shown) will likely have the on die termination connected between the Vcc voltage from voltage regulator 12 and GTL signal line 18. As the number of IC 2 GTL signal lines 18 that are not pulled down to ground increases, the current flow from Vcc voltage regulator 12 to Vtt voltage regulator 14 may increase. Generally, most voltage regulators require a minimum amount of current to be sourced by the regulator for the voltage regulator to stay within the proper voltage regulation range. If most or all of the signals from IC 2 are pulled up through the termination devices, enough current may flow from Vcc voltage regulator 12 to Vtt voltage regulator 14 through the termination devices such that the minimum regulation current requirement for Vtt voltage regulator 14 is not met and, therefore, voltage regulator 14 shuts down. This may cause system problems, for example, unacceptable noise signal levels within the system.
A solution to this problem is to remove the current path between the voltage regulators. However, removing the current path may not be an option due to the fact that the design of already existing motherboards cannot be easily changed in the field and the need for on die termination with the new ICs. The motherboards have already been designed and currently may exist with termination on the motherboard. Therefore, the motherboard would need to be reworked when an IC with on die termination is inserted.
A further possible solution is to set the voltage regulators to voltages that will not cause current flow from the Vcc voltage regulator to the Vtt voltage regulator. However, setting both voltage regulators to voltages that will not cause current flow would likely require the Vcc voltage regulator to be set lower and possibly not allow for optimum IC performance (e.g., raising the Vcc voltage generally results in improved IC performance).
Therefore, a need exists for an arrangement allowing a semiconductor IC device with termination on the die that can be substituted for a semiconductor IC device with termination not on the die attached to an existing motherboard of an electronic system, and not have any potential for voltage regulators shutting off and causing system problems.